Autostereoscopic display device and display method

ABSTRACT

An autostereoscopic display comprises a steerable display backlight, comprising a light output arrangement for providing lines of light output and a first lenticular lens array, with each lens focused near a corresponding line of light output. A display panel is illuminated by the backlight and a second lenticular array generates at least two views to different viewing directions. Head and/or eye tracking is used for tracking at least two viewers. Views are provided to the two eyes of a tracked viewer at the same time, and views are provided to the two eyes of different tracked viewers time-sequentially.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2016/082723, filed on Dec.27, 2016, which claims the benefit of EP Patent Application No. EP15203021.9, filed on Dec. 29, 2015. These applications are herebyincorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to an autostereoscopic display device and adisplay method.

BACKGROUND OF THE INVENTION

A known autostereoscopic display device comprises a two-dimensionalliquid crystal display panel having a row and column array of displaypixels (wherein a “pixel” typically comprises a set of “sub-pixels”, anda “sub-pixel” is the smallest individually addressable, single-color,picture element) acting as an image forming means to produce a display.An array of elongated lenses extending parallel to one another overliesthe display pixel array and acts as a view forming means. These areknown as “lenticular lenses”. Outputs from the display pixels areprojected through these lenticular lenses, which function to modify thedirections of the outputs.

The lenticular lenses are provided as a sheet of lens elements, each ofwhich comprises an elongate part-cylindrical lens element. Thelenticular lenses extend in the column direction of the display panel,with each lenticular lens overlying a respective group of two or moreadjacent columns of display sub-pixels.

Each lenticular lens can be associated with two columns of displaysub-pixels to enable a user to observe a single stereoscopic image.Instead, each lenticular lens can be associated with a group of three ormore adjacent display sub-pixels in the row direction. Correspondingcolumns of display sub-pixels in each group are arranged appropriatelyto provide a vertical slice from a respective two dimensional sub-image.As a user's head is moved from left to right a series of successive,different, stereoscopic views are observed creating, for example, alook-around impression.

FIG. 1 is a schematic perspective view of a known direct viewautostereoscopic display device 1. The known device 1 comprises a liquidcrystal display panel 3 of the active matrix type that acts as a spatiallight modulator to produce the display.

The display panel 3 has an orthogonal array of rows and columns ofdisplay sub-pixels 5. For the sake of clarity, only a small number ofdisplay sub-pixels 5 are shown in the Figure. In practice, the displaypanel 3 might e.g. comprise about two thousand rows and four thousandcolumns of display sub-pixels 5. In the future this might even becomemuch more. In a black and white display panel a sub-pixel in factconstitutes a full pixel. In a color display a sub-pixel is one colorcomponent of a full color pixel. The full color pixel, according togeneral terminology comprises all sub-pixels necessary for creating allcolors of a smallest image part displayed. Thus, e.g. a full color pixelmay have red (R) green (G) and blue (B) sub-pixels possibly augmentedwith a white sub-pixel or with one or more other elementary coloredsub-pixels. The structure of the liquid crystal display panel 3 isentirely conventional. In particular, the panel 3 comprises a pair ofspaced transparent glass substrates, between which an aligned twistednematic or other liquid crystal material is provided. The substratescarry patterns of transparent indium tin oxide (ITO) electrodes on theirfacing surfaces. Polarizing layers are also provided on the outersurfaces of the substrates.

Each display sub-pixel 5 comprises opposing electrodes on thesubstrates, with the intervening liquid crystal material there between.The shape and layout of the display sub-pixels 5 are determined by theshape and layout of the electrodes. The display sub-pixels 5 areregularly spaced from one another by gaps.

Each display sub-pixel 5 is associated with a switching element, such asa thin film transistor (TFT) or thin film diode (TFD). The displaypixels are operated to produce the display by providing addressingsignals to the switching elements, and suitable addressing schemes willbe known to those skilled in the art.

The display panel 3 is illuminated by a light source 7 comprising, inthis case, a planar backlight extending over the area of the displaypixel array. Light from the light source 7 is directed through thedisplay panel 3, with the individual display sub-pixels 5 being drivento modulate the light and produce the display. The backlight 7 has sideedges 7 a and 7 b, a top edge 7 c and a bottom edge 7 d. It has a frontface from which light is output. The display device 1 also comprises alenticular sheet 9, arranged over the display side of the display panel3, which performs a light directing function and thus a view formingfunction. The lenticular sheet 9 comprises a row of lenticular elements11 extending parallel to one another, of which only one is shown withexaggerated dimensions for the sake of clarity.

The lenticular elements 11 are in the form of convex (part-) cylindricallenses each having an elongate axis 12 extending perpendicular to thecylindrical curvature of the element, and each element acts as a lightoutput directing means to provide different images, or views, from thedisplay panel 3 to the eyes of a user positioned in front of the displaydevice 1.

The display device has a controller 13 which controls the backlight andthe display panel.

The autostereoscopic display device 1 shown in FIG. 1 is capable ofproviding several different perspective views in different directions,i.e. it is able to direct the pixel output to different spatialpositions within the field of view of the display device. In particular,each lenticular element 11 overlies a small group of display sub-pixels5 in each row, where, in the current example, a row extendsperpendicular to the elongate axis of the lenticular element 11. Thelenticular element 11 projects the output of each display sub-pixel 5 ofa group in a different direction, so as to form the several differentviews. As the user's head moves from left to right, his/her eyes willreceive different ones of the several views, in turn.

FIG. 2 shows the principle of operation of a lenticular type imagingarrangement as described above in more detail and shows the backlight20, the display device 24, the liquid crystal display panel and thelenticular array 28 in cross section. FIG. 2 shows how the lenticular 27of the lenticular arrangement 28 directs the outputs of the pixels 26′,26″ and 26′″ of a group of pixels to the respective three differentspatial locations 22′, 22″ and 22′″ in front of the display device. Thedifferent locations 22′, 22″ and 22′″ are part of three different views.

In a similar manner, the same output of display pixels 26′, 26″ and 26′″is directed into the respective three other different spatial locations25′, 25″ and 25′″ by the lenticular 27′ of the arrangement 28. While thethree spatial positions 22′ to 22′″ define a first viewing zone or cone29′, the three spatial positions 25′ to 25′″ define a second viewingcone 29″. It will be appreciated that more of such cones exist (notshown) depending on the number of lenticular lenses of the array thatcan direct the output of a group of pixels such as formed by the pixels26′ to 26′″. The cones fill the entire field of view of the displaydevice.

FIG. 2 is only schematic. The adjacent cones 29′ and 29″ result fromrays intersecting adjacent lens surfaces at corresponding positions, notshown in schematic FIG. 2.

The above view directing principle leads to view repetition occurringupon going from one viewing cone to another as within every cone thesame pixel output is displayed in a particular view. Thus, in theexample of FIG. 2, spatial positions 22″ and 25″ provide the same view,but in different viewing cones 29′ and 29″ respectively. In other words,a particular view shows the same content in all viewing cones. At theboundaries between viewing cones, there is a jump between extreme views,so that the autostereoscopic effect is disrupted.

A solution to this problem is to allow only a single viewing cone, forexample by designing the backlight to have a directional output. WO2011/145031 discloses various approaches for defining a display with asingle cone output.

The use of a collimated backlight for controlling the direction fromwhich a view can be seen is for example known for several differentapplications, including for gaze tracking applications, privacy panelsand enhanced brightness panels. One known component of such a collimatedbacklight is a light generating component which extracts all of itslight in the form of an array of thin light emitting stripes spaced ataround the pitch of a lenticular lens that is also part of thebacklight.

This configuration is shown in FIG. 3 in which the backlight 7 comprisesan array 30 of striped light emitters, a positive lens array 32 and areplica structure 34 between the lens array and the emitters. The lensarray 32 collimates the light coming from the array 30 of thin lightemitting stripes. Such a backlight can be formed from a series ofemissive elements, such as lines of LEDs or OLED stripes.

It is very challenging to provide correct images for the left and righteyes of every viewer so that a stereoscopic viewing experience iscreated for a wide range of viewing angles and viewing distances.

The generation of a large number N of views as repeating “fans” in thehorizontal direction as explained above, by using a (slanted) lenticulararray in front of the display, provides one solution. However, awell-known disadvantage of this solution is that the 3D mode spatialresolution is strongly reduced—commonly by a factor of the square rootof N in each direction. Furthermore, the stereoscopic experience is lostfor a viewer at the transition edge between adjacent fans of views.Hence, there are diamond-shaped viewing zones that are determined by thecone angle and screen width of the display and viewers have to find agood place to sit and are not able to move much without reducing their3D experience.

Multi-view and especially fractional view displays provide a smoothmotion parallax and smooth cone transitions, but at the cost ofrendering many views (e.g. 10, 20, etc.). Often a low amount such as oneor two inputs views is available and multiple synthetic views aregenerated. In a fractional view display the well-known problem ofappearance of dark bands caused by the black mask around the sub-pixelsis eliminated or at least reduced by dimensioning a lenticular lensarray such that the relative position of the sub-pixels and lens axesresults in multiple (k) sub-phases. This suppresses the lower spatialfrequencies of the banding by averaging over the k partial view points.In addition the extra view points allow for smooth motion parallax andfine-grained viewer adjustments. Such a fractional view display isdisclosed in U.S. Pat. No. 8,134,590 and its contents is hereby includedby reference, especially the part from column 1, line 45 to column 2line 6.

Alternatively, a computer graphics method (e.g. OpenGL) is used torender views. In this way, conventional autostereoscopic displaysgenerate much more information than needed for providing the stereoimages for the left and right eyes of every viewer.

This problem is partially solved in so-called “stereo on multiview”displays with eye and/or head tracking, where only two views arerendered in alignment with the position of a single viewer, such thatthe viewer perceives a stereoscopic effect according to the two views.Thus the cost of generating the views is reduced because only two viewsare generated, or entirely removed when two input views are readilyavailable. The problem with these devices is that they are only suitablefor a single user, because any other non-tracked user would typicallysee a distorted image.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to an example, there is provided an autostereoscopic displaycomprising:

a steerable display backlight, comprising a light output arrangement forproviding lines of light output and a first lenticular lens array;

a display panel having an array of display sub-pixels for producing adisplay image, the display illuminated by the backlight;

a second lenticular lens array for generating at least two views todifferent viewing directions;

a head and/or eye tracking system for tracking at least two viewers; and

a controller for controlling the display panel and the steerable displaybacklight, wherein the controller is adapted to provide views to the twoeyes of a tracked viewer at the same time, and to provide views to thetwo eyes of different tracked viewers time-sequentially.

The autostereoscopic display can be high resolution by providing a smallnumber of views (as a result of the head/eye tracking). It enables amulti-user and dead-zone free display. Each viewer is individuallyaddressed via a light steering backlight that is directing light to onlyone face at a time. The views to each individual viewer may be providedwith a small viewing cone to provide optimum images for the left andright eyes of each viewer. However, the backlight output does not needto be so narrow that it reaches only one eye of a viewer. Instead, thebacklight output is sufficiently wide to cover both eyes of a viewer (atthe intended viewing distance) but not so wide as to cover multipleviewers. The mean inter-ocular distance for the general population is 63mm, whereas when viewers sit next to each other, the distance betweenthe nearest eyes of the two viewers is typically at least 500 mm. Thus,the cone width of the display at the intended viewing distance is forexample in the range 100 mm to 500 mm, for example 100 mm to 300 mm, forexample 100 mm to 150 mm.

The at least two views for each viewer are based on spatial multiplexingwhereas the views for different viewers are based on temporalmultiplexing.

Each lenticular lens of the backlight preferably has a focus at or neara corresponding line of light output, for example the focal distance isequal to 0.7 to 1.3 times the distance between the backlight lenticularlens and the lines of light output.

In one implementation, the controller is adapted to provide views to thetwo eyes of a tracked viewer by assigning the input views per sub-pixelaccording to the estimated visibility of each sub-pixel for the left andright eye of the viewer. The visibility is estimated based on anestimate of the position of the viewer with respect to the display. Thevisibility relates to the extent to which a particular sub-pixel isprojected by a lens of the second lenticular array towards a particularviewing location.

A small number of views reduces the image processing requirements. Ithas also been found that using at least 4 static views is sufficient tohide the transition between views, as a user moves laterally. This worksbecause each eye of the user is in one or between two adjacent views andthose two views are then assigned to the same input view.

It is instead possible to generate to only two dynamic views for thedisplay. In this case, a shifting arrangement may be provided for(electro-optical, mechanical or otherwise) shifting the secondlenticular lens (the one that generates the multiple views) relative tothe display. The controller is then adapted to provide views to the twoeyes of a tracked viewer which are selected from the only two possibleviews, and the controller is adapted to control the shifting of thesecond lenticular relative to the display.

The steerable display backlight may have an output beam which has anangular spread of less than tan⁻¹(5IOD/vd) where IOD is the inter-oculardistance and vd is the intended viewer distance from the display. Thismeans the width of the output beam at the intended viewer distance isless than 5 times the inter-ocular distance. This avoids adjacentviewers being displayed the same images. The output beam may have anangular spread of between tan⁻¹(1.5IOD/vd) and tan⁻¹(3IOD/vd), forexample tan⁻¹(2IOD/vd).

The head and/or eye tracking system may be for locating the distance tothe viewer and the lateral position of the viewer with respect to thedisplay panel.

A diffuser may be provided on one side of the display panel. Thisreduces intensity modulations.

Examples in accordance with another aspect provide an autostereoscopicdisplay method comprising:

tracking at least two viewers of the display;

providing lines of backlight light output in dependence on the trackedviewer locations;

directing the lines of backlight output through a first lenticular lensarray to provide directional control;

illuminating a display panel comprising an array of display sub-pixelsusing the directionally controlled backlight light output to produce adisplay image;

generating at least two views to different viewing directions using asecond lenticular lens array, wherein views are provided to the two eyesof a tracked viewer at the same time, and views are provided to the twoeyes of the different tracked viewers time-sequentially.

This provides the display of autostereoscopic images to one viewer at atime, but with simultaneous display to the two eyes of each viewer.

The method may comprise assigning the input views to a number of viewsof at least 4 and/or less than 10, for example less than 8. The inputviews are then assigned per sub-pixel according to an estimatedvisibility of each sub-pixel for the left and right eye of the viewer.

Alternatively, the method may comprise generating two views andproviding the two views to the two eyes of a tracked viewer, wherein themethod further comprises shifting the second lenticular lens arrayrelative to the display.

A backlight output beam may be provided which has an angular spread ofless than tan⁻¹(5IOD/vd) where IOD is the inter-ocular distance and vdis the intended viewer distance from the display.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, purely by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of a known autostereoscopicdisplay device;

FIG. 2 is a schematic cross sectional view of the display device shownin FIG. 1;

FIG. 3 shows a known directional backlight design using stripedemitters;

FIG. 4 shows the approach of this invention in simple schematic form;

FIG. 5 shows the optical components in more detail;

FIG. 6 shows the viewer's intraocular angle Φ_(IOD) and display coneangle in air Φ0_(c) and view angle Φ0_(v);

FIG. 7 shows the relationships between the display geometry and displaycone angles;

FIG. 8 shows the overlap of adjacent views of the display;

FIG. 9 shows a cross-section of the display panel;

FIG. 10 shows the overlap of adjacent views of the backlight output;

FIG. 11 shows the angular intensity distribution of the display;

FIG. 12 a backlight cone angle and illuminated width as output from theoverall backlight;

FIG. 13 shows a specific design of backlight in more detail;

FIG. 14 shows the angular profiles of 8 views of the backlight of FIG.13;

FIG. 15 shows the overlap of adjacent and near-nearest views of thebacklight of FIG. 13;

FIG. 16 shows the angular intensity of the backlight with all lightstripes on;

FIG. 17 shows a smoothed angular intensity profile of the backlight byusing a diffuser sheet;

FIG. 18 shows the angular profiles of 8 views (left image) and the viewoverlaps (right image) when using a 1.3° diffuser sheet for comparisonwith FIGS. 14 and 15;

FIG. 19 shows a most difficult viewer arrangement for the display tofunction in which there is a left viewer and a right viewer;

FIG. 20 illustrates the intensities for the views illuminating the leftand right viewers;

FIG. 21 shows the intensity of a two view system as a function ofviewing angle;

FIG. 22 shows the intensity for the two view system as a function of thelateral position with respect to the screen;

FIG. 23 shows how the views are switched between 0 and 1 for the twoeyes.

FIG. 24 shows a view quality parameter as a function of viewingdistance;

FIG. 25 corresponds to FIG. 22 but for three views;

FIG. 26 shows how the views are switched between 0, 1 and 2 for the twoeyes;

FIG. 27 shows the view quality parameter as a function of viewingdistance for FIG. 25;

FIG. 28 corresponds to FIG. 22 but for four views; and

FIG. 29 shows how the views are switched between 0, 1, 2 and 3 for thetwo eyes; and

FIG. 30 shows the view parameter as a function of viewing distance forFIG. 28.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention provides an autostereoscopic display which comprises asteerable display backlight having a light output arrangement forproviding lines of light output and a first lenticular lens array, witheach lens focused near a corresponding line of light output. A displaypanel is illuminated by the backlight and a second lenticular arraygenerates at least two views to different viewing directions. Headand/or eye tracking is used for tracking one or more viewers of thedisplay. Views are provided to the two eyes of a tracked viewer at thesame time, and, in case of more than one viewer, views are provided tothe two eyes of different tracked viewers time-sequentially. The numberof necessary views can be reduced when there is the ability to move theviews using optics (in addition to backlight steering).

The invention enables a reduction in image processing by enabling fewerviews than for a standard multi-viewer multiple cone display, but italso enables operation for multiple viewers.

FIG. 4 shows the approach in simple schematic form. The displaycomprises a light modulating display panel 40 such as an LCD panel and alight steering backlight 41. The display provides a first sub-frame 42directed to a first viewer 44 and a second sub-frame 46 directed to asecond viewer 48. Within each sub-frame views are providedsimultaneously to the two eyes of the viewer. The system can beimplemented using standard components and does not require theproduction of a narrow beam in the backlight. This makes the systempractical to implement.

The system makes use of detection of viewer locations, in particular thehorizontal viewing angle and preferably also the distance to the viewervia eye/head tracking by head tracking unit 49. A light steeringbacklight is used to direct the sub-frames into the desired direction.In one example, the light steering backlight comprises light emanatingstripes near the focal plane of a lenticular lens array. The relativeposition of the stripes and an associated lens dictates the direction inwhich the stripe-shaped beam is output from the backlight. Thus byselecting the light emitting stripes to illuminate, directional controlis possible.

A 3D lenticular display panel 40 with a second lenticular lens array isused to create the multiple images (two of which images are combined bythe viewer to perceive a stereoscopic image) with a small viewing cone.The width of the viewing cone at the intended location of the viewer isfor example about twice the intraocular distance (IOD) to provideoptimum stereo images for the left and right eyes of each viewer.

The function of the backlight 41 is to illuminate each viewer one byone, making use of the head and/or eye tracking unit 49. The displaypanel 40 then provides stereoscopic vision to a single viewer.

A control unit 50 calculates the viewpoint of each eye of each viewer.The backlight stripes to be actuated in each sub-frame are selected andviews are assigned to the display panel 40. The display has leastcrosstalk when the viewing cone is quite narrow, and preferably the halfcone angle should correspond to the angle formed by the intraoculardistance and the viewing distance.

FIG. 5 shows the optical components in more detail.

The backlight 41 comprises an array of illuminating stripes 51, with thestripes extending in the display column (i.e. vertical) direction. Thebacklight is provided with a first lenticular array 52, which alsocomprises elongate lenses which extend in the column direction. Adiffuser 53 is shown over the backlight lens array 52 and may beconsidered to be part of the backlight 41. This diffuser is optional,and it may in fact be behind or in front of the display panel (so it mayinstead be considered to be part of the display panel). It spreads outthe backlight views to reduce intensity modulations. The diffuser canspread wider than the intensity profile of a view (or even full cone) ofthe display.

The focal plane of the lens array 52 is preferably at the light emittingstripes 51. More generally, the lenticular lenses of the backlightpreferably have a focus at or near a corresponding line of light output,for example the focal distance is equal to 0.7 to 1.3 times the distancebetween the backlight lenticular lens and the lines of light output.

The display panel 40 is provided over the backlight 41.

A second lenticular array 54 is spaced from the display panel 40 and isused in conventional manner to generate multiple viewing directions, asshown in FIG. 2.

The refractive index values of the various layers are shown in FIG. 5.The lenticular arrays are formed of a material having higher refractiveindex (n=1.53 in this example such as an acrylic material) than thematerial used in the spacing between them (n=1.41 in this example suchas a silicone material).

By way of example, the lens layer material may comprise an acrylicmaterial including: 80% Ethoxylated bisphenol A diacrylate (SR-349 from“Sartomer Company, Inc”) and 20% trimethylolpropane triacrylate (TMPTA)with a refractive index of around 1.53. The spacer layer is made of asilicone rubber material (Elastosil RT604 from “Wacker chemicals Inc”)with a refractive index of around 1.41. Other materials with appropriaterefractive indices may be used.

A detailed design will now be presented including example parameters andoptical simulations for an autostereoscopic TV display, but theinvention is suitable for a wide range of viewing distances, screendiagonals and display resolutions.

1. 3D lenticular display 40, 54

A 3D lenticular display is desired with a low loss of spatial resolutionwhile still providing an optimum stereoscopic experience for eachviewer.

The views for a given viewer (which may be considered to be contentviews) are all provided at the same time, i.e. in one sub-frame withlight directed by the backlight towards that particular viewer. Theintended use of the display according to the invention is to supply atleast two views (left and right), which are possibly viewer-dependent,e.g. taking into account the viewer perspective. For example, if thedisplay is for generating only two views, then the views may not beviewer-dependent, but if more views are generated by the display, theviews for selection to display to the viewer may be viewer-dependent.The supplied views are matched to the display views (of which there areat least two but there may be many), based on the viewer position anddisplay parameters/calibration, using a view assignment and weavingstep. This might involve mixing of left and right views per sub-pixel orsimply picking either left or right per sub-pixel. Thus, the two viewsto be displayed to the viewer are selected from or derived from a set ofdisplay views for the 3D scene being rendered.

There are different options to realize these aims:

(i) A known slanted lenticular design with a low number of views, butpreferably at least 4 and for example less than 10. The reason forpreferring a low number of views is to reduce the spatial resolutionloss. The reason for preferring the use of at least 4 views is that eacheye of a user is in one or between two adjacent views and those twoviews are then assigned to the same input view. When the user moveslaterally it is possible to reassign content views (e.g. left and rightinput view) without the user noticing. A low number N of views with agood distribution of resolution for RGB-striped panels is for exampleobtained based on:

Number of views N=5, display lenticular pitch p_(H)=5*p_(sp) wherep_(sp) is the sub-pixel pitch, lenticular lens slant angle α=tan⁻¹(⅓).

This design has the disadvantage of “banding” but this can becompensated.

(ii) A “stereo on multiview” design with a higher number of (fractional)views N_(f)>10, where the software rendering bundles several displayviews into two “effective” views for the left and right eye of eachviewer. In this way a good spatial resolution is maintained whereasbanding effects are minimized. The larger number of (fractional) viewsalso provides more flexibility, for instance to increase the usableviewing range or to follow lateral movement of the user more precisely,enabling a smaller viewing cone.

(iii) A stereo “eye following” lenticular with steerable opticalelements, such as electrowetting lenses, lenses moved or deformed byactuators made of electroactive polymers, variable Gradient Index Lenses(GRIN) made of liquid crystal materials and electrodes, etc. Thechallenge for this option is the required fast switching of opticalcomponents. This option relates to a stereo concept (i.e. exactly twoviews: left eye and right eye views), where active optical componentsare used to exactly position the two views on the two eyes of theviewer.

There are few known lenticular designs with N<10 and good 3D properties,i.e. separate addressability of left and right eye, good spatialdistribution of 3D pixels, little banding, etc.

In one example an N=5 view design is chosen with slant angle α=tan⁻¹(⅓)for rectangular sub-pixels with a height-to-width ratio of 3 which aresurrounded by 10% of black matrix. The horizontal display lens pitchp_(H) is thus 5 times the sub-pixel pitch p_(sp). For this design, the3D resolution loss is equally distributed over the horizontal andvertical directions, i.e. equal to a factor of the square root of 5=2.24in both directions.

A 4 K high definition display would thus have in 3D mode operation aresolution slightly worse than a full HD (FHD) display.

Assuming a 48 inch (122 cm) 16:9 display geometry, the display has widthdw=107 cm and display height dh=60 cm. The standard viewing distance isvd=3*dh=180 cm.

For a 4 K high definition display there are 3840 pixels per row and eachpixel is divided into 3 sub-pixels for the colors red, green and blue.

The sub-pixel pitch p_(sp) is thus p_(sp)=dw/(3*3840)=92.88 μm.

The horizontal display lens pitch is p_(H)=N*p_(sp)=464.4 μm.

The orthogonal (true) display lens pitch is then p=p_(H)*cos(α)=440.6 μmand thus simply determined by the display resolution and width dw andthe number of views N.

FIG. 6 shows the viewer's intraocular angle Φ_(IOD) and display coneangle in air Φ0_(c) and view angle Φ0_(v).

The distance “e” between the display panel and display lens arrangement(shown in FIG. 5) is determined from the demand that the viewer'sintraocular angle Φ_(IOD) should correspond to about twice the displayview angle Φ0_(v). This is important, because this N=5 view design showsinevitably some overlap between adjacent views and it is chosen tocenter near-nearest views onto the viewer's eye pair:Φ_(IOD)=2*tan⁻¹(IOD/(2*vd))=2.062°

This gives a display view angle Φ0_(v)≈Φ_(IOD)/2=1.0°.

The display cone angle in air Φ0_(c) is N times Φ0_(v) orΦ0_(c)=5*Φ0_(v)=5.0°.

FIG. 7 shows the relationships between the display geometry and displaycone angles Φ2_(c) and Φ0_(c)

The “inner” display cone angle Φ2_(c) is obtained from Φ0_(c) usingSnell's law Φ2_(c)=2*sin⁻¹((1/n2_(d))*sin(Φ0_(c)/2))=3.55° (here:n2_(d)=1.41).

Finally, the distance e between the display 41 and the lenticular arrayis given by:e=p/(2*tan(Φ2_(c)/2))=7.12 mm

A slightly increased value such as e=7.5 mm in this example may be usedto compensate for the decrease of the intraocular angle Φ_(IOD) fornon-central viewing positions of the viewer. In this way a proper 3Dviewing experience is ensured throughout the whole illuminated widthΔx_(ill) of the backlight (discussed further below).

To realize small overlap of views and low banding for a wide viewingangle, for example aiming for ±35°, a lenticular design is chosen withlenses having a small radius of curvature and small refractive indexdifference across the lens surface. This type of lens is described indetail in WO 2009/147588 A1.

As already shown in FIG. 5, n2_(d)=1.41 and n1_(d)=1.53.

The paraxial focus of the second lenticular 54 must not be placed tooclose to the display panel, because this would lead to strong overlap ofnear-nearest views at large viewing angles and increased banding at lowangles.

This issue is shown in FIG. 8 which shows the overlap of adjacent views(plot 70) and next-nearest views (plot 72) of the display for f=7.56 mm(e/f˜100%).

A view of view number “a” is adjacent to a view of view number “b” ifa=b±1. A view of view number “a” is “next nearest” to a view of viewnumber “b” if a=b±2. The overlap for two completely separated views iszero, and the overlap for two identical views is defined as 100%. Theoverlap of views becomes greater at greater viewing angles.

The overlap of views a and b is defined as:

${{Ovl}( {a,b} )}==\frac{\int{{{{Int}_{a}({\varphi 0})} \cdot {{Int}_{b}({\varphi 0})}}d\;{\varphi 0}}}{\sqrt{{{Int}_{a}({\varphi 0})}^{2}d\;{\varphi 0}} \cdot \sqrt{{{Int}_{b}({\varphi 0})}^{2}d\;{\varphi 0}}}$

The function Int_(x) is the function which defines the (simulated)intensity of view “x” as a function of the angular coordinate φ0

The display optics may be set at a moderate under focus (for examplee/f˜75%). With this setting, the overlap of next-nearest views at largeangles is minimized, because the display is at the position of the“minimum root-mean-square” focus at these angles.

FIG. 9 shows a cross-section of the display panel for this TV example.All measures are in mm.

The radius of curvature R of the display is chosen as R=0.85 mm yieldinga paraxial focal length f=n2_(d)*R/(n2_(d)−n1_(d))=10.02 mm.

In FIG. 9, the line 90 represents the so-called paraxial focus. It isconstructed from the intersections of adjacent rays that impinge uponthe lens surface close to the center of the lens and which originatefrom a given direction behind the lens. As shown, rays from largerviewing angles which impinge around the center of the lens focus nearerto the lens than rays from the normal direction. The views provided tolarger viewing angles are generated by the display at a location whichis further from the focus of the lenticular lens 54.

The line 92 represents the locus of those points where the Root MeanSquare (RMS) width of the beam is smallest.

The line 94 represents the so-called caustic tip. It is constructed fromthe intersections of adjacent rays that hit the lens surfaceperpendicularly. It represents the furthest location from the lens wherethese rays cross, so that after this caustic tip, all rays arediverging.

FIG. 9 shows the location of the display panel 40 and the display lenses54 with one lens center shown as 55.

With this particular setting of focal length (f=10.02 mm) the overlap atlarge angles is significantly reduced with respect to FIG. 8. This canbe seen in FIG. 10, which is based on the same parameters as FIG. 8,i.e. f=10.02 mm (e/f˜75%).

Furthermore, the angular intensity distribution of the display optics ismore homogeneous over the whole viewing range (covering the displaycentral viewing cone and about 16 viewing cone repetitions). This isshown in FIG. 11, which plots the angular intensity of the 3D displaywith all views “on”. Angles beyond 40° have not been simulated.

2. Light Steering Backlight 41

The backlight is designed to provide an illuminated width Δx_(ill) whichis as large as possible while still being able to individually addressthe face of each viewer. This implies that the “cone angle” of thebacklight Φ0_(cb) should be maximized while a low overlap ofnext-nearest backlight “views” should be maintained.

To maximize the cone angle, the distance of the backlight lenticular 52from the light emanating stripes e_(b) (see FIG. 5) should be minimizedfor a given backlight lenticular pitch p_(b).

To create a low overlap the backlight light stripes should be located asclose as possible to the focus of the backlight lenticular.

Taking both conditions together the aim is thus to minimize the focallength f_(b)=n2_(b)*R_(b)/(n2_(b)−n1_(b)) of the backlight lenticular.f_(b) is minimized if the difference n2_(b)−n1_(b) is maximized bychoosing n1_(b)=1 (=air) and n2_(b)=1.53 (Trimethylolpropane triacrylate(TMPTA)-based material as disclosed above) or higher (for example forpolycarbonate n=1.58) and at the same time minimize the radius ofcurvature R_(b).

For a circular cross-section of the lenticular elements, the minimumradius of curvature is given by R_(b)=p_(b)/2. A mild under-focus(e_(b)/f_(b)˜85%) is advantageous to maintain a moderate overlap (˜20%)of adjacent backlight views to be able to illuminate a viewer's face atany possible location.

In this way the relative backlight dimensions e_(b) and R_(b) aredetermined as multiples of the backlight pitch p_(b).

The absolute backlight dimensions are determined by the pitch of thelight emanating stripes p_(s) and the number of backlight “views”nv_(b), because p_(b)=p_(s)*nv_(b).

The number of views nv_(b) is calculated as the ratio of illuminatedwidth Δx_(ill) and the viewer's face width fw: nv_(b)=Δx_(ill)/fw. Thereis one remaining degree of freedom, i.e. the pitch of the light stripesp_(s).

This degree of freedom can be used to minimize moiré-like angularintensity fluctuations which are arising from the combination of twolenticular arrays. It has been proven advantageous to adjust thebacklight dimensions in such a way that the ratio of the horizontal lenspitches of backlight p_(b) and display p_(H) is an integer multiple Nplarger than 1 and smaller than 6: p_(b)=Np*p_(H), 1<Np<6.

The banding effect due to the black matrix between the light emanatingstripes is minimized, if the lens centers of backlight and display areat the same lateral position for even values of N, but shifted byp_(H)/2 (i.e. backlight lens center and display lens edges at the samelateral position) for odd values of N.

FIG. 12 shows the backlight cone angle and illuminated width as outputfrom the overall backlight 41. It also shows dimensions within thebacklight. Assuming a 48″ (122 cm) 16:9 display geometry a display widthdw=107 cm and display height dh=60 cm, the standard viewing distance isvd=3*dh=180 cm. The center of illumination at the display edges isinclined by an angle β=tan⁻¹(dw/(2*vd))=16.5°. The cone angle of thebacklight Φ0_(cb) should be as large as possible (for example 70°) tohave a large illuminated width Δx_(ill).

A backlight cone angle of 70° would thus correspond to an illuminatedwidth:Δx _(ill)=2·(vd·tan(Φ0_(cb)/2−β)+dw/2)=229 cm

Assuming that the viewer's face width is fw=15 cm it is necessary toprovide nv_(b)=Δx_(ill)/fw=16 backlight “views” with an angular width of70°/16=4.4°. If the light emanating stripes have a width of 100 μm andare surrounded by 25% black matrix then the pitch of the light stripesis 125 μm and the pitch of the backlight lenticular is p_(b)=125μm*nv_(b)=2.00 mm.

The distance of the backlight lenticular 52 from the light stripes isderived from the backlight cone angle as e_(b)=2.455 mm.

As shown in FIG. 12, the inner cone angle between the backlight stripeand lens Φ2_(cb)=2*tan⁻¹(p_(b)/(2*e_(b)))=44.3°. The backlight coneangle is given by:Φ0_(cb)=2*sin⁻¹(n2b*sin(Φ2_(cb)/2))=70.5°.

For a circular cross-section of the lenticular elements the minimumradius of curvature is given by R_(b)=p_(b)/2=1.00 mm and the focallength is f_(b)=2.89 mm.

This specific design of backlight is shown in FIG. 13. As in FIG. 9, allmeasures are in mm and the same reference numbers are used as in FIG. 9for the paraxial focus 90, caustic tip 94, minimum RMS focus 92. FIG. 13shows the location of the backlight stripes 41 and the backlight lenses52 (with lens center 53).

When performing a ray tracing simulation for the backlight the viewshave good angular profiles as shown in FIG. 14 with moderate overlap(˜20%) of adjacent views. FIG. 14 shows the angular profiles of 8 viewsof the backlight and FIG. 15 shows the overlap of adjacent andnext-nearest views of the backlight.

FIG. 16 shows the angular intensity of the backlight with all lightstripes on and it shows that the design does have some banding, i.e.angular intensity oscillations if all light stripes are on.

This banding can be suppressed if desired by adding a diffuser sheet ontop of the backlight lenticular as shown in FIG. 5. Assuming a Gaussianangular profile of the diffuser with a standard deviation wd=1.3° thesmoothed angular intensity profile of the backlight is shown in FIG. 17.

Of course, by introducing a diffuser, the individual views are broadenedand overlaps are increased, but not in an excessive manner because theviews are already very wide.

FIG. 18 shows the angular profiles of 8 views (left image) and the viewoverlaps (right image) when using a 1.3° diffuser sheet for comparisonwith FIGS. 14 and 15.

The applicability of this backlight concept can be demonstrated byconsidering a worst case situation.

This situation is shown in FIG. 19. There are two viewers 190, 192sitting shoulder to shoulder, i.e. 50 cm apart, at a viewing distancevd=180 cm from the screen. The right viewer 192 is located at the rightedge of the illuminated width. Both viewers are observing the left edgeof the display, so that the viewing angles are 25.3° and 16.7°,respectively.

The angular separation of the adjacent eyes is thus 25.3°−16.7°=8.6°,i.e. about 2 backlight view widths (=4.4°). This is sufficient to ensurea small overlap of intensities.

This is shown in FIG. 20 which illustrates the intensities for the viewsilluminating the left viewer (plot 190 a) and the right viewer (plot 192a). The overlap (evaluated at the centers of the plots 190 a and 192 a)is small.

As mentioned above, there are various options for the number of views ofthe 3D scene which are generated and how they are processed to createthe pair of views to be displayed to an individual viewer. The optionsdepend on how many views are generated by the combination of the displaypanel and the second lenticular lens.

If the second lenticular lens array is a 2-view lens, then thecontroller has to shift the lens in order to steer the views to theuser.

If the second lenticular lens array is a multi-view lens (more than twoviews), then the controller has to assign the content views to thesub-pixels of the display panel such that the left content view isvisible in the left eye, and the right content view in the right eye.This operation is typically called view assignment, weaving orinterleaving.

The image content has views, including at least one for the left and onefor the right eye. For example, the display may be used to play aBlu-ray 3D disc with stereoscopic content. The views might also berendered to take into account the perspective of the user, for instancewith 3D games (so the user can look around corners).

The backlight also provides view generation, but this is in the form oflight bundles because they are not necessarily pixelated. In eachsub-frame, some backlight stripes are turned on such that light bundleis created for the eyes of one viewer, but not the others.

Backlight stripes might be segmented to enable local dimmingfunctionality to improve dynamic contrast ratio. Local dimming is oftenused in high-end 2D LCD televisions.

The sub-system formed by the combination of the display panel and thesecond lenticular lens combination generates projected views. This couldbe a two-view lens with shifting or a multi-view, possibly slanted,fractional lens with stereo rendering.

FIG. 21 shows the intensity (in arbitrary units) of a two view system onthe y-axis as a function of viewing angle (in degrees, on the x-axis).By “two view system” is meant a single stereo pair of views, i.e. 2rendered views.

Position zero corresponds to a normal position relative to the displayscreen. Plot 210 is the intensity distribution for one view and plot 212is the intensity distribution for the other view. The two views aresomewhat overlapping so that there are only moderate intensityvariations when moving the head sideways.

FIG. 22 shows the intensity (in arbitrary units) for the two view systemon the y-axis as a function of the lateral position of the viewer's facewith respect to the screen (in cm, on the x-axis). The observed screenpoint is considered at the central position (x=0).

In FIG. 22 there are two views; named view 0 and view 1. The faceposition on the x-axis denotes the x-position of the tip of the nose ofthe viewer. Each curve shows the intensity of each view entering eacheye, hence 4 curves. For example, the curve L0 is the intensity of view0 entering the left eye. R1 is the intensity of view 1 entering theright eye. Similarly L1 is the intensity of view 1 entering the left eyeand R0 is the intensity of view 0 entering the right eye.

At an optimum face position (e.g. at face position 0) L0 is at itsmaximum and L1 is near zero so that view 0 can be presented to the lefteye. At the same face position, R1 is at its maximum and R0 is near zeroso that so that view 1 can be presented to the right eye. At a faceposition around 6 cm L1 is at its maximum and L0 is near zero, so theimage intended for the left eye will then be switched to view 1. At thesame face position, R0 is at its maximum and R1 is near zero, so theimage intended for the right eye will then be switched to view 0.

Between these positions, for example at around 3 cm, all intensities areabout equal (L0=L1=R0=R1). This means that for any choice of switchingthe images (left image onto view 0 and right image onto view 1 or viceversa) each eye would see the same content, i.e. both images, and the 3Dviewing effect is lost.

The intensity distributions are shown for the intended (designed)viewing distance.

To produce an autostereoscopic effect, the views are switched such thatfor each eye, the view with the higher intensity is addressed. Thus, theinput views (i.e. the image content) are assigned per sub-pixelaccording to the estimated visibility of each sub-pixel for the left andright eye of the viewer. A sub-pixel which is imaged by the secondlenticular to the right eye is assigned a pixel of the right eye imagecontent, and a sub-pixel which is imaged by the second lenticular to theleft eye is assigned a pixel of the left eye image. As explained withreference to FIG. 2, the relative position of each sub-pixel beneath the(second) lenticular lens determines the direction to which the sub-pixelis imaged. The visibility is estimated based on an estimate of theposition of the viewer with respect to the display.

A view parameter can be defined of the relative strength of theintensity of the desired view compared to the undesired view (or views):

$h_{3D} = \frac{I_{good} - I_{bad}}{I_{good} + I_{bad}}$where I_(good)=Intensity intended for that eye and I_(bad)=Intensityintended for the other eye.

FIG. 23 shows how the views (the view number is on the y-axis) areswitched between 0 and 1 for the two eyes. Plot 230 is for the right eyeand plot 232 is for the left eye.

FIG. 24 shows the view parameter defined above as a function of lateralviewing distance from the center, with plot 240 for the left eye andplot 242 for the right eye. It shows that there are equally spacedpositions where the 3D experience is lost. This is an inevitableconsequence of working with only two fixed views.

One of the options outlined above is to use steerable optical elementswith eye tracking to follow the face.

The alternative is to use fixed optical elements and use more than twoviews.

FIG. 25 corresponds to FIG. 22 but for three views. Again, the intensitydistributions are shown as function of the lateral position of theviewer's face when observing a screen point at position x=0.

L0 is the intensity distribution for presenting view 0 to the left eye.L1 is the intensity distribution for presenting view 1 to the left eye.L2 is the intensity distribution for presenting view 2 to the left eye.R0 is the intensity distribution for presenting view 0 to the right eye.R1 is the intensity distribution for presenting view 1 to the right eye.R2 is the intensity distribution for presenting view 2 to the right eye.

FIG. 26 shows how the views (the view number is on the y-axis) areswitched between 0, 1 and 2 for the two eyes. Repeating plot 260 is forthe right eye and repeating plot 262 is for the left eye.

FIG. 27 shows the view parameter as a function of the lateral viewingdistance, for the two eyes.

FIG. 27 shows that an improved but not optimum 3D experience is possiblewith 3 fixed views. This is a consequence of the overlap of adjacentviews and the fact that always adjacent views are switched to the leftand right eye.

It has been found that using at least 4 views enables a high qualityautostereoscopic viewing experience.

FIG. 28 corresponds to FIG. 22 but for four views. Again, the intensitydistributions are shown as a function of the lateral position of theviewer's face when observing a screen point at position x=0.

L0 is the intensity distribution for presenting view 0 to the left eye.L1 is the intensity distribution for presenting view 1 to the left eye.L2 is the intensity distribution for presenting view 2 to the left eye.L3 is the intensity distribution for presenting view 3 to the left eye.R0 is the intensity distribution for presenting view 0 to the right eye.R1 is the intensity distribution for presenting view 1 to the right eye.R2 is the intensity distribution for presenting view 2 to the right eye.R3 is the intensity distribution for presenting view 3 to the left eye.

The next adjacent views (R=L±2) can thus be switched to the left andright eye.

FIG. 29 shows how the views (the view number is on the y-axis) areswitched between 0, 1, 2 and 3 for the two eyes. Repeating plot 290 isfor the right eye and repeating plot 292 is for the left eye.

FIG. 30 shows the view parameter as a function of the lateral viewingdistance, for the two eyes. It shows that an optimum 3D experience isindeed possible with at least 4 fixed views.

3. Other Design Considerations

Even when the display is designed for a certain viewing distance (e.g.180 cm), still due to the large viewing cone of the backlight, thedisplay is fully usable for a large viewing range. When moving closer(to about ⅔ of the viewing distance), more backlight views are inbetween the viewers, which increases the number of backlight viewsbetween the viewers and thus reduces crosstalk in between the viewers.The limit is determined by the autostereoscopic display because thecrosstalk in between the left and right eye will increase and the stereoeffect will fully diminish when there is one viewing cone in between theeyes of the viewer (typically at ½ of the intended viewing distance).When the actual viewing distance is larger than intended, then therewill be less backlight views and the autostereoscopic views between theviewers and both intrapersonal and interpersonal crosstalk willgradually increase with distance.

The above example performs well at 4/3 of the intended distance. It alsodepends on the content whether this crosstalk is visible. To someextent, a wide viewing angle and a large viewing distance range can betraded for each other by tuning lens parameters.

As is clear from the description above, the display optics is generallydesigned for one particular viewing distance. However, one advantage isthe additional possibility to adapt the view rendering to a wide rangeof viewing distances, because the different viewers are addressed timesequentially. When a viewer is closer to the display (e.g. at ⅔ of theoptimum distance), the angular distance between his eyes will beincreased (by a factor of 3/2), therefore the optimum 3D experience canbe maintained if the view rendering will increase the view indexdifference between both eyes by the same factor (from 2 to 3). Theopposite can be implemented when a viewer is at a larger distance fromthe display (e.g. at 4/3 of the optimum distance). This adaptation maybe implemented by using different rendering of the set of display imagesto generate the views to be presented to the tracked viewer.

The viewing distance (the position of the eyes) is also used todetermine which backlight stripes to illuminate. The light beams shouldbe generated to converge at that viewing distance such that the displayis uniformly visible for a viewer at that position. This is known asviewing distance correction. When the physical lens pitch is denoted p,then the render pitch is p′ is derived according to:p′/p=(V+D)/V

where V is the viewing distance and D is the optical thickness. Theoptical thickness is the (integral of the) physical thickness divided bythe index of refraction. The correction is small but significant, e.g.V=1 m, D=2 mm gives p′/p=1.002.

Typically the lens arrays used are plano convex because this is easierto manufacture, but it is possible to laminate two arrays in perfectalignment to produce a combined convex lens array. This allows forproducing stronger lenses, and this in turns allows for reducing theaberrations that cause the tails in the intensity distributions of thebacklight views, or for increasing the viewing angle of the display. Italso allows for using lower index differences and this reduces haze dueto reflections in the backlight unit.

As explained above, the maximum radius of curvature for a cylindricallens is half the lens pitch. The eccentricity of the lens can be raisedfrom 0 (circle) to 1 (parabolic) or in between (elliptical). The effectof raising the lens eccentricity is that a smaller radius of curvaturecan be used and that the lens is less thick, but at the cost ofincreasing the tails of the intensity profiles of the backlight views.By way of example a suitable value is an eccentricity in the range of0.3 to 0.5, for example 0.4.

The invention may be used in autostereoscopic displays for multi-userdevices such as computer monitors, TVs and signage applications.

Optionally there are other measures to reduce intensity modulations inthe backlight, such as backlight stripes that run in a checkerboardpattern (to hide the black matrix), in combination with a holographicdiffuser that diffuses strongly orthogonal to the lens direction to hidethe backlight structure. Optionally, multiple diffusers may be combinedin a single (holographic) diffuser.

The detailed example and simulations above apply to one specificintended application (a 122 cm TV display). The specific design valuesare purely by way of example, and these details have been presentedsimply to enable the design issues to be understood. The concepts canthen be applied to other designs.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality. The mere fact that certain measures are recited inmutually different dependent claims does not indicate that a combinationof these measures cannot be used to advantage.

Any reference signs in the claims should not be construed as limitingthe scope.

The invention claimed is:
 1. An autostereoscopic display, comprising: asteerable display backlight, wherein the steerable display backlightcomprises: a light output arrangement, wherein the light outputarrangement is arranged to provide a plurality of lines of light output,and a first lenticular lens array, wherein each lenticular lens of thefirst lenticular lens array has a focal distance which is between 0.7and 1.3 times a distance from the lenticular lens to a correspondingline of light output among the plurality of lines of light output; adisplay panel, wherein the display panel has an array of sub-pixels forproducing an image, and wherein the display panel is configured to beilluminated by the backlight; a second lenticular lens array, whereinthe second lenticular lens array is arranged to generate at least twoviews in different viewing directions; a head tracking system, whereinthe head tracking system is arranged to track one or more viewers eachhaving two eyes; and a controller circuit, wherein the controllercircuit is arranged to control the display panel and the steerabledisplay backlight, wherein the controller circuit is arranged to controlthe autostereoscopic display to provide two views to the two eyes of atracked viewer at the same time, and wherein the controller circuit isfurther arranged such that, in a situation where there are two trackedviewers, the controller unit controls the autostereoscopic display toprovide two views to the two eyes of a first tracked viewer in a firstsub-frame and to provide two additional views to the two eyes of asecond tracked viewer in a second sub-frame subsequent to the firstsub-frame.
 2. The display of claim 1, wherein the second lenticular lensarray is arranged to provide at least four views, wherein the controllercircuit is arranged to provide the two views to the two eyes of thetracked viewer by assigning at least two input views per sub-pixelaccording to an amount by which the second lenticular lens arrayprojects an output from each sub-pixel to estimated locations of a lefteye and a right eye of the tracked viewer.
 3. The display of claim 1,wherein the second lenticular lens array is arranged to provide morethan ten fractional views, wherein the controller circuit is arranged toprovide the two views to the two eyes of the tracked viewer by assigningat least two input views per sub-pixel according to an amount by whichthe second lenticular lens array projects an output from each sub-pixelto estimated locations of a left eye and a right eye of the trackedviewer.
 4. The display of claim 1, further comprising a shiftingarrangement, wherein the shifting arrangement is arranged to shift thesecond lenticular lens array relative to the display, wherein thecontroller circuit is arranged to control the shifting of the secondlenticular lens array relative to the display panel.
 5. The display ofclaim 1, wherein the steerable display backlight has an output beamwhich has an angular spread of less than tan⁻¹(5IOD/vd), wherein IOD isa mean inter-ocular distance for the general populace, and wherein vd isone third of a height of the display.
 6. The display of claim 5, whereinthe output beam has an angular spread of between tan⁻¹(1.5IOD/vd) andtan⁻¹(3IOD/vd).
 7. The display of claim 1, wherein the head trackingsystem is arranged to locate a distance to the tracked viewer, and tolocate a lateral position of the tracked viewer, with respect to thedisplay panel.
 8. The display of claim 1, comprising a diffuser on oneside of the display panel.
 9. The display of claim 1, wherein thecontroller circuit is configured to control the steerable displaybacklight such that in a first sub-frame the steerable display backlightoutputs a first cone of light in a first direction toward a firsttracked viewer and outputs no cone of light toward a second trackedviewer, and wherein the controller circuit is configured to control thesteerable display backlight such that in a second sub-frame subsequentto the first sub-frame the steerable display backlight outputs a secondcone of light in a second direction toward the second tracked viewer andoutputs no cone of light toward the first tracked viewer.
 10. A methodof autostereoscopic display, comprising: tracking one or more viewers;providing at least one line of a backlight light output from a lightoutput arrangement in dependence on one or more corresponding locationsof the tracked one or more viewers, wherein the light output arrangementis configured to selectively produce a plurality of lines of lightoutput; directing the at least one line of backlight light outputthrough a first lenticular lens array, wherein the directing is arrangedto provide directional control of the backlight light output, andwherein each lenticular lens of the first lenticular lens array has afocal distance which is between 0.7 and 1.3 times a distance from thelenticular lens to a corresponding line of light output among theplurality of lines of light output; illuminating a display panel withthe directionally controlled backlight light output from the firstlenticular lens array, wherein the display panel comprises an array ofsub-pixels, wherein the illuminating uses the directionally controlledbacklight light output to produce an image; generating two views todifferent viewing directions using a second lenticular lens array;providing two views to the two eyes of a tracked viewer at the sametime; and in a situation where there are two tracked viewers, providingthe two views to the two eyes of a first tracked viewer in a firstsub-frame and providing two additional views to the two eyes of a secondtracked viewer in a second sub-frame subsequent to the first sub-frame.11. The method of claim 10, further comprising assigning at least twoinput views per sub-pixel according to an amount by which the secondlenticular lens array projects an output from each sub-pixel to theestimated locations of a left eye and a right eye of the tracked viewer,wherein the generating comprises generating at least four views.
 12. Themethod of claim 10, further comprising assigning at least two inputviews per sub-pixel according to an amount by which the secondlenticular lens array projects an output from each sub-pixel toestimated locations of a left eye and a right eye of the tracked viewer,wherein the generating comprises generating less than 10 views.
 13. Themethod of claim 10, further comprising shifting the second lenticularlens array relative to the display panel.
 14. The method of claim 10,further comprising providing a backlight output beam, wherein the outputbeam has an angular spread of less than tan⁻¹(5IOD/vd), wherein IOD is amean inter-ocular distance for the general populace, wherein vd is onethird of a height of the display.
 15. The method as claimed in claim 10,further comprising: locating a distance to the tracked viewer withrespect to the display panel; and locating a lateral position of thetracked viewer with respect to the display panel.
 16. The method ofclaim 10, further comprising: in a first sub-frame, the steerabledisplay backlight outputting a first cone of light in a first directiontoward a first tracked viewer and outputting no cone of light toward asecond tracked viewer; and in a second sub-frame interval subsequent tothe first sub-frame, the steerable display backlight outputting a secondcone of light in a second direction toward the second tracked viewer andoutputting no cone of light toward the first tracked viewer.
 17. Anautostereoscopic display, comprising: a steerable display backlight,wherein the steerable display backlight comprises: a light outputarrangement, wherein the light output arrangement is arranged to providea plurality of lines of light output, and a first lenticular lens array,wherein each lenticular lens of the first lenticular lens array has afocal distance which is between 0.7 and 1.3 times a distance from thelenticular lens to a corresponding line of light output among theplurality of lines of light output; a display panel, wherein the displaypanel has an array of sub-pixels for producing an image, and wherein thedisplay panel is configured to be illuminated by the backlight; a secondlenticular lens array, wherein the second lenticular lens array isarranged to generate at least two views in different viewing directions;an eye tracking system, wherein the eye tracking system is arranged totrack eyes of one or more viewers; and a controller circuit, wherein thecontroller circuit is arranged to control the display panel and thesteerable display backlight, wherein the controller circuit is arrangedto control the autostereoscopic display to provide two views to the twoeyes of a tracked viewer at the same time, and wherein the controllercircuit is further arranged such that, in a situation where there aretwo tracked viewers, the controller circuit controls theautostereoscopic display to provide the two views to the two eyes of afirst tracked viewer in a first sub-frame and to provide two additionalviews to the two eyes of a second tracked viewer in a second sub-framesubsequent to the first subframe.
 18. The display of claim 17, whereinthe eye tracking system is arranged to locate a distance to the trackedviewer, and to locate a lateral position of the tracked viewer, withrespect to the display panel.
 19. The display of claim 17, wherein thecontroller circuit is configured to control the steerable displaybacklight such that in the first sub-frame the steerable displaybacklight outputs a first cone of light in a first direction toward afirst tracked viewer and outputs no cone of light toward a secondtracked viewer, and wherein the controller circuit is configured tocontrol the steerable display backlight such that in a second sub-framesubsequent to the first sub-frame the steerable display backlightoutputs a second cone of light in a second direction toward the secondtracked viewer and outputs no cone of light toward the first trackedviewer.